1. Technical Field
The present invention relates generally to internal combustion engines and, more particularly, to a misfire detection apparatus and method for detecting misfire of individual cylinders in an internal combustion engine.
2. Discussion
The Clean Air Act (1955) required motor vehicle manufacturers to reduce exhaust emissions of carbon monoxide, hydrocarbons, and oxides of nitrogen from light duty motor vehicles. To comply with the Act, most motor vehicle manufacturers generally use catalytic converters on production vehicles to control such exhaust emissions. A catalytic converter typically includes a catalyst and operates at a very high temperature in order to burn unwanted byproducts of combustion so as to reduce hydrocarbons, carbon monoxide and nitrous oxide. However, increased amounts of unburned byproducts that often remain after the occurrence of an engine misfire can lead to damage of the catalytic converter.
More recently, regulatory agencies have proposed that passenger, light-duty and medium-duty motor vehicles with feedback fuel control systems be equipped with a malfunction indicator signal that will inform the motor vehicle operator of any malfunction of an emission-related component that interfaces with an on-board computer of the motor vehicle. It is also proposed or required that an on-board diagnostic system identify the likely area of malfunction. Proposals or requirements have set forth catalyst, misfire, evaporative purge system, secondary air system, air conditioning system refrigerant, fuel system, oxygen sensor, exhaust gas recirculation, and comprehensive component monitoring requirements.
As previously mentioned, misfire of internal combustion engines can cause damage to the catalyst of a catalytic converter. With respect to misfire, the identification of the specific cylinder experiencing misfire may be required. Some regulations provide that the motor vehicle manufacturer specify a percentage of misfires out of the total number of firing events necessary for determining malfunction for: (1) the percent misfire evaluated in a fixed number of revolution increments for each engine speed and load condition which would result in catalyst damage; (2) the percent misfire evaluated in a certain number of revolution increments which would cause a durability demonstration motor vehicle to fail a Federal Test Procedure (FTP) by more than 150% of the applicable standard if the degree of misfire were present from the beginning of the test; and (3) the degree of misfire evaluated in a certain number of revolution increments which would cause a durability demonstration motor vehicle to fail an inspection and maintenance (IM) program tailpipe exhaust emission test.
Current and proposed future regulations are also requiring that motor vehicle manufacturers be able to provide information detailing the occurrence of misfires such as identifying which cylinders are responsible for one or more misfires. The misfire information need be collected and stored in memory so that the stored information may be downloaded at a service center and used to determine the cause of misfires in the vehicle. One misfire detection and identification approach is disclosed in issued U.S. Pat. No. 5,361,629 issued Nov. 8, 1994 and titled "Single Sensor Misfire Detection Apparatus and Method for an Internal Combustion Engine". The above-cited patent is also hereby incorporated by reference. The misfire detection approach in the above-cited patent senses rotation of a crankshaft and calculates a crankshaft velocity based on the sensed rotation. The calculated crankshaft velocity or a compensated velocity is compared to a predetermined crankshaft velocity range to determine if misfire occurred.
When an engine cylinder misfires, a corresponding drop in engine speed will normally result. A relatively large drop in engine speed is usually indicative of a misfire event. However, a number of engine operating conditions may result in transients which sometimes tend to give the same effect as a misfire, even though a misfire event did not occur for the corresponding cylinder at issue. One example of a transient condition may occur when harsh clutching maneuvers are performed on a vehicle equipped with a manual transmission. When this occurs, torsional forces and vibrations transmitted through the engine crankshaft are induced to the engine speed pickup and may actually be large enough to read as misfire events with some conventional misfire detection approaches. Additionally, the occurrence of a misfire event for a corresponding cylinder can sometimes cause transients within the engine or vehicle which in turn may be sensed and detected as false misfires.
It is therefore one object of the present invention to provide for an improved apparatus and method of detecting cylinder misfires in an internal combustion engine.
It is another object of the present invention to provide for a misfire detection apparatus and method which is capable of detecting cylinder misfires for an internal combustion engine and which is capable of filtering out unwanted noise caused by engine transients to thereby reduce possible false engine misfire reports.
It is yet another object of the present invention to provide for a misfire detection apparatus and method which reduces the noise effects that can be caused by the occurrence of a misfire event.
It is a further object of the present invention to provide for a misfire detection apparatus and method which compensates for normal engine accelerations, and realizes a good signal to noise ratio.